Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 210300

Area Forecast Discussion
National Weather Service Gaylord MI
1100 PM EDT Mon Mar 20 2017

Issued at 1025 PM EDT Mon Mar 20 2017

Evening surface map reveals intial cold front now well east of the
state with weak sfc/low level ridging attempting to nose into
region. Stronger cold front/push of colder air is swinging down
through Ontario and will arrive Tuesday. Better moisture/higher
dewpoint air still lingers across lower Michigan (dewpoints still
largely in the 30s) although there is a wedge of low level dry air
nosing across northern Wisconsin and the U.P. and now starting to
bleed down into northern lower Michigan (PLN/SLH dewpoints have
dropped into the lower 20s).

Meanwhile, band of post-frontal mid level cloud cover driven by
low-mid FGEN continues to slide through lower Michigan this
evening. We have one narrow band of elevated precip swing through
the region earlier...producing largely sprinkles. Still some
leftover weak-ish forcing occurring along and south of the M-55
corridor producing pockets of elevated returns.

Rest of tonight: Low-mid level deformation axis weakens/slips
south allowing N-S clearing trend to proceed. We have lingering
light showers/sprinkles across the SE part of the CWA through
midnight or so...which looks fine although I may tweak that just a
bit based on trends.

Upstream, stronger cold front will arriving into eastern upper/NW
lower Michigan early Tuesday morning and there may already be some
synoptic and lake response snow showers sneaking into eastern
upper by morning. It will be close, but I will keep sct pops going
for snow showers for eastern upper Michigan after 09Z.


.NEAR TERM...(Tonight)
Issued at 339 PM EDT Mon Mar 20 2017

...Falling temperatures expected Tuesday with cold front passage...

High Impact Weather Potential: Minimal

Pattern Synopsis/Forecast: Current surface/composite analysis shows
an old cold front/surface trough moving across the forecast area at
early afternoon...extending south to a 1012mb low over northeast
Missouri.  Narrow west-east oriented surface ridge axis follows this
trough...with a more substantial cold front over far northwest
Ontario/southern portions of Manitoba and Saskatchewan.  Elongated
potential vorticity anomaly supporting said cold front extends from
James Bay west along the cold frontal baroclinic zone then arcs
northwestward across central Saskatchewan/northern Alberta.  Water
vapor imagery shows a decent looking vorticity center embedded
within this PV anomaly digging southeast across Saskatchewan toward
Lake Winnipeg.  Despite a broad area of cold advection/isentropic
descent occurring across Wisconsin/Upper of broken
light rain showers stretched from eastern Upper southwest into
northeast Wisconsin...driven primarily by low/mid level
frontogenesis occurring along the northern edge of steeper mid level
lapse rates (e.g., 12Z DVN sounding)...and some weakly difluent flow
aloft.  Drier air is spreading southeast behind the cloud/
precipitation band across northern Minnesota/northern Lake Superior.

Primary Forecast Concerns: Light showers will continue to advance
across northern Lower Michigan through mid evening...with some hints
that things may linger around Saginaw Bay through midnight or so.
Skies are expected to clear behind this cloud band and ahead of
approaching cold front and Lake Winnipeg vorticity center that will
spin its way across Lake Superior overnight.  NAM-WRF/RAP soundings
hinting at some fog/stratus development this evening along the St.
Mary`s River...but looks suspiciously like a model-induced drop in
temperatures where the guidance thinks ice cover is located on the
lakes (seeing these cold spots in low temperatures across Whitefish
Bay/St. Mary`s River as well as across and west of the Straits into
northern Lake Michigan where observed ice cover is located).

Vorticity center crossing Lake Superior may bring a brief shot of
light snow showers/flurries to eastern Upper toward daybreak.  This
will be followed by the cold front and a quick drop in temperatures
across Lake Superior/Upper Michigan during the morning (and early
high temperatures before the mercury drops during the afternoon).
Will also see an increasing in lake and diurnally induced cloud
cover and flurries/snow showers across the Upper Peninsula Tuesday
morning...then down into northwest Lower later Tuesday afternoon.
Gusty northwest winds also expected with arrival of cold
advection...with gusts 25-30+mph anticipated.  Should be a wide
range in temperatures Tuesday...with readings falling into the 20s
by late morning across eastern Upper...while temperatures are
expected to warm into the 40s across at least the southeast third of
the forecast area.


.SHORT TERM...(Tuesday and Wednesday)
Issued at 339 PM EDT Mon Mar 20 2017

...Brief Shot of Cold Air...

High Impact Weather Potential...Nothing.

Pattern Synopsis/Forecast...One last piece of arctic air will drop
into the Great Lakes/New England midweek in response to building
ridge over the plains.  850mb temperatures drop briefly to -18 to
-20c Tuesday night, only slowly recovering into the day on
Wednesday. No downstream blocking (much like this entire winter),
so this will be a quick cooldown followed by building heights/
warmer weather for the end of the week. Bone dry airmass with
modified arctic high pressure building southward into the Great
Lakes. Possibly some weakish north/northeast flow light lake
effect activity Tuesday night, but it won`t amount to much.
Otherwise, not much in the way of sensible weather concerns. Great
radiational cooling set-up for midweek, so some very cold
overnight lows both Tuesday night and Wednesday, likely single
digits in many areas. If we had much in the way of snowcover left,
below zero readings would be more likely. Coldest day of the week
will be Wednesday, with many areas remaining in the 20s.

Thermal trough slides east by Thursday with quickly warming
temperatures aloft.  So after a cold start to the day, readings
likely working into the upper 30s to middle 40s.   A few warm air
advection mid clouds possible on Thursday, otherwise lots of

Primary Forecast Concerns...Very little.  Will have to see if we are
able to generate much of any lake effect snow showers Tuesday night,
given the incredibly dry boundary layer airmass.  The only other
forecast concern will be low temperatures - how low will they go?

.LONG TERM...(Wednesday night through Monday)
Issued at 339 PM EDT Mon Mar 20 2017

High Impact Weather Potential...Minor, but with the potential for a
wintry mix increasing Friday.

At upper levels, nearly zonal flow at 500mb will persist across the
Great Lakes through much of the forecast period, as a cutoff upper
low from the Plains lifts toward the Ohio Valley. The upper low will
exit east Monday, allowing a narrow ridge to redevelop over the
region to begin the upcoming work week. Mid level temps in this
pattern will warm from around -2c/-3c early Friday to generally
between 0c and +4c through the weekend, which should generate nearly
seasonal afternoon highs in the 40s across northern Michigan. At the
surface, a storm system organizing over the central Plains will lift
toward the Great Lakes Friday and Saturday. This system will become
nearly washed out over the Ohio Valley Sunday between two large
areas of high pressure, one near Hudson Bay and the second over the
Atlantic. This system will generate a period of wintry mix over
northern Michigan Friday through Sunday. High pressure near Hudson
Bay will then settle into the Great Lakes to begin the upcoming work
week, generating some sun and mild temperatures over northern
Michigan Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1100 PM EDT Mon Mar 20 2017

VFR conditions anticipated through tonight. Remaining band of mid
and high cloud cover will clear our through the overnight hours.
some patchy fog is possible across parts of northern lower
Michigan early as, as surface dewpoints remain on the higher side
and temps cool. but wedge of drier air spreading down through
northern lower Michigan should end any fog threat.

Another cold front (and push of substantially colder air) will
slide down through northern Michigan on Tuesday. This will likely
bring the return of a BKN lower cloud deck Tuesday morning, and
there may be a period of MVFR cigs as the colder air bleeds into
the region, but daytime heating should tend to mix out cloud cover
through the afternoon. Otherwise, colder air will gin up sct-bkn
lake effect clouds and probably some light snow showers that will
impact parts of NW lower Michigan (primarily TVC) late Tuesday
morning through the afternoon. Loss of heating Tuesday night may
lead to better organized lake clouds and snow showers and cigs
dipping back below 3K feet.


Issued at 339 PM EDT Mon Mar 20 2017

Cold advection behind a passing cold front will allow winds to ramp
up from the northwest starting Tuesday morning...which should result
in widespread Small Craft Advisory conditions within nearshore zones...
could be some gale force winds within the Straits to Thunder Bay
nearshore region on northern Lake Huron with coastally convergent
flow. Winds will begin to diminish Tuesday high
pressure builds across the upper Great Lakes.


LH...SMALL CRAFT ADVISORY from 6 AM Tuesday to midnight EDT Tuesday
     night for LHZ345-346.
     SMALL CRAFT ADVISORY from 6 AM Tuesday to 6 AM EDT Wednesday for
     GALE WARNING from 6 AM Tuesday to 6 AM EDT Wednesday for LHZ347-
LM...SMALL CRAFT ADVISORY from 6 AM Tuesday to midnight EDT Tuesday
     night for LMZ341.
     SMALL CRAFT ADVISORY from 6 AM Tuesday to 6 AM EDT Wednesday for
LS...SMALL CRAFT ADVISORY from 6 AM Tuesday to midnight EDT Tuesday
     night for LSZ321-322.


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